Don’t be deceived by appearances – that’s the lesson a young Tallaght man wants readers to take away from his heart-warming post about his dinner with a homeless man.

Liam Marum posted the photo on Facebook last night after an encounter with a homeless man didn’t turn out how he expected.

He wrote that he was approached by the man, named Nathan, in the car park of Tallaght Shopping Centre on Wednesday evening after work.

When asked if he had some change for a burger, Mr Marum initially told him, “No mate, I’m sorry, I’ve no change.”

“No problem sir and thanks very much, I apologise for asking you, have a great day,” Nathan replied, before walking off across the car park.

“I paused for a minute, then looked to see where he was walking to,” Mr Marum wrote, noting that he headed toward McDonald’s.

“To me this guy was genuine and hungry. My first thought (was) ‘he's maybe a junkie looking to score his next fix’.”

However, after he drove over to McDonald’s, he spotted Nathan searching on the ground for coins.

“I pulled up beside him and said, ‘sorry mate but sometimes I'm sceptical of giving money to people who seem to be homeless and ask for spare change, my reason is, I think people just use the money for their next fix or alcohol’.”

Mr Marum offered to buy him a burger in McDonald’s, and told him to order whatever he liked off the menu.

“He ordered a Big Mac Meal. The customer assistant asked, ‘Would you like to go large?’ Nathan looked at me and I smiled,” he said.

“I said, ‘go ahead mate, no problem’. He even had the manners to ask. Nathan couldn't stop saying thanks and when receiving his €6.99 Meal, he was so polite in asking the customer assistant for salt and ketchup.”

Mr Marum joined Nathan while he ate, where he learned more about the circumstances that lead to him becoming homeless.

“Nathan told me he lost his brother two years ago and his sister took her own life over a month ago. He is now sleeping rough at the back of a school or college, in a sleeping bag! My heart went out to this guy,” he said.

The pair took a picture together, which Mr Marum shared on Facebook along with his account of their dinner.

The post has since been shared 9,500 times and received hundreds of likes and comments from people inspired by the story.

Mr Marum told Independent.ie he was shocked by the reaction to his post.

"I wasn't expecting it go to viral, but if it opens people's eyes a little and someone can benefit from it, then I'm happy," he said.

"It's not about me, it's about Nathan and other people like him."

In his Facebook post, he wrote that he wanted to share the story “to bring to the attention of the public that, not all homeless people are junkies or thieves or beggars”, in an attempt to “give people a different view” on the issue.

“There (are) some who are genuinely suffering and need support. Where's he going to get his next meal from and what challenges does he continue to face daily?

“It only took 20 minutes of my time and a few euro to help this lad and actually sit and speak with him for a bit.”

He added that as he got up to leave, Nathan said, “Thanks so much Liam and God bless you”.

“Those few words meant a lot to me,” Mr Marum said.

“I'm just trying to give one of our own Irish citizens a dig out. Who knows when your luck could change... Never judge a book by its cover!”